1. Field of the Invention
The invention relates to the field of composite structure fabrication and, in particular, to a method of manufacturing foam filled honeycomb core parts.
2. Description of Related Art
The manufacture of complex contoured parts from foam reinforced honeycomb is typically accomplished by loading the pieces of the core with the foam, curing the foam and bonding the pieces together, and thereafter machining to the final shape. This method is normally required because it is difficult to uniformly load honeycomb core having a very large depth. In addition, extremely large pieces of honeycomb core are expensive to manufacture.
This process has several significant disadvantages. The first being that the bonding of pieces of core together creates discontinuities, and therefore weakening the overall strength of the finished part. Secondly, if the finished part is thin and has a large contoured shape, a lot of material is wasted. Thirdly, in low observable structures for aircraft and the like, such discontinuities can effect the radar signature of the vehicle or structure.
What is desired is a method of manufacturing foam filled honeycomb core structures.
What is further desired is a method of manufacturing foam filled honeycomb core structures having a complex contour.
The desired method of manufacturing foam filled honeycomb core structures provides a complex contour with a minimum of wasted material.
The desired manufacturing method provides foam filled honeycomb core structures having a complex contour with no internal discontinuities.
The present disclosure relates to a method of making a foam filled honeycomb core structure having at least a partially curved shape. In detail, the method includes the steps of providing a honeycomb core billet. The billet is then reinforced by filling it with a foam. Thereafter the foam filled billet is placed on a mold having a curved mold surface. The foam filled billet is then creep formed to the general shape of the structure by applying a load thereto. The weights used for creep forming are typically applied to the foam filled billet at the point where maximum deformation is to occur. In addition, the mold is positioned such that the point where the load is applied to the foam filled billet and the point on the mold at the center of curvature are vertically aligned. Finally, the now curved foam filled billet is machined to the final shape of the structure.
If the foam is of the type that can be readily softened by heating to a moderately high temperature, such as a cross-linked polystyrene, it is heated to a temperature above its glass transition temperature prior to or during creep forming. This may require that the foam filled billet be vacuum bagged to prevent degradation by exposure to oxygen in the air.
The novel features which are believed to be characteristic of the invention, both as to its organization and method of operation, together with further objects and advantages thereof, will be better understood from the following description in connection with the accompanying drawings in which the presently preferred embodiment of the invention is illustrated by way of example. It is to be expressly understood, however, that the drawings are for purposes of illustration and description only and are not intended as a definition of the limits of the invention.